Hydraulic turbine shaft current differential protection device and method for accurately locating fault point

Abstract

The application provides a water turbine shaft current differential protection device and method for accurately positioning fault points, and relates to the technical field of safety protection of hydro-generator units. The application is provided with double current transformers for collecting total current of a water turbine shaft and backflow current of a grounding carbon brush, and the collected current is sent to a main control unit after synchronous sampling. A three-section self-adaptive braking algorithm is used to dynamically generate a protection action threshold, and a four-dimensional fault positioning combination criterion is used to realize accurate partition identification of upper guide bearing and water guide / lower guide bearing faults. The device hardware is composed of a double-CT collection unit, a high-speed collection unit, a main control unit, a man-machine interaction unit, a multi-way output unit, a communication unit and a wide-temperature isolation power supply. The application solves the industry problem that the traditional single-CT shaft current protection criterion is single, anti-interference is poor and the fault point cannot be positioned, breaks the technical barrier that conventional differential protection cannot be used for shaft current protection, and greatly reduces the misoperation probability caused by stray current and carbon brush leakage through the self-adaptive braking structure.

Description

Technical Field

[0001] This invention relates to the field of safety protection technology for hydro-generator sets, specifically to a differential protection device and method for hydro-turbine shaft current that accurately locates fault points. Background Technology

[0002] The turbine generator unit must have its bearing shaft current protection or shaft insulation monitoring circuit properly engaged, and long-term operation without protection is strictly prohibited. Currently, the shaft current protection of hydropower stations generally adopts single CT over-limit protection, which has the following defects: 1) The judgment criteria are singular, relying solely on over-limit alarms, resulting in poor anti-interference capability; 2) Grounding carbon brush leakage current and stray current are prone to causing false tripping; 3) It is impossible to locate the fault point of the upper conductor and water conductor, resulting in low maintenance efficiency; 4) It lacks braking characteristics, the action boundary is ambiguous, and the reliability is insufficient.

[0003] Currently, the industry-standard shaft current protection relies on a single current transformer connected in series in the unit's grounding carbon brush circuit. It only collects the total shaft current, a single electrical quantity. Its operating logic involves real-time acquisition of the effective value of the shaft current, pre-setting a current action threshold, and directly triggering an alarm or protection output when the acquired current value exceeds the preset value. It lacks multi-quantity collaborative calculation logic and fault zoning capabilities. This solution has been widely adopted due to its simple hardware wiring and low cost, enabling basic fault early warning when the shaft current significantly exceeds the limit, thus meeting basic safety production needs in early hydropower operation and maintenance systems.

[0004] The differential protection principle has been maturely applied to fault protection of electrical equipment such as transformers, transmission lines, and busbars in power systems. It relies on the difference in electrical quantities on both sides to distinguish between faults inside and outside the zone, and has the advantages of accurate fault identification and distinguishing between faults inside and outside the zone. However, due to the limitations of the electrical characteristics of the turbine shaft current itself and the grounding structure of the unit, the industry has long reached a technical consensus: conventional differential protection cannot be adapted to the turbine shaft current operating conditions, and the dual-CT differential architecture has never been implemented in the shaft current protection scenario, becoming a long-term technical gap in the field of hydropower protection.

[0005] Currently, single-CT over-limit shaft current protection has several shortcomings: 1. Single protection criterion and weak anti-interference performance: It only uses the shaft current amplitude exceeding the limit as the sole action criterion, lacking multi-parameter collaborative verification logic. Various interferences in the field environment can easily cause abnormal rises in the measured current, leading to malfunctions of the protection. 2. Stray leakage current induces frequent maloperations: Leakage current in the contact gap of the unit's grounding carbon brush, stray current coupled by harmonics in the unit's excitation system, and stray current induced by the main shaft rotation can all cause false exceedances in the sampling current, which is the primary cause of frequent false alarms and trips in the field, seriously interfering with the normal operation of the unit. 3. Lack of fault location differentiation capability and low maintenance efficiency: It can only determine that the shaft current is abnormal in the whole unit, and cannot distinguish whether the fault occurs in the upper guide bearing, water guide bearing, or lower guide bearing. After a fault occurs, maintenance personnel need to disassemble and check each bearing component one by one, which is time-consuming and results in significant downtime losses. 4. Lack of adaptive braking logic and rigid action threshold: The setting value is a factory-fixed parameter and cannot dynamically adjust the threshold according to the unit load, spindle speed, and bearing lubrication oil film operation status. The sensitivity is too low under light load conditions and minor insulation hazards cannot be detected; the threshold is too low under heavy load and strong interference conditions, and it is very easy to malfunction without reason. The protection action boundary is vague and the operation reliability is poor.

[0006] Existing general-purpose power differential protection cannot be directly applied to turbine shaft current protection. Several long-standing technical challenges in the industry are key reasons why dual-CT differential solutions have been slow to be implemented in the shaft current field: 1. The characteristics of the measured current signal contradict the applicable conditions of conventional differential protection: Turbine shaft current is a weak current in the microampere to milliampere range, exhibiting low-frequency, non-periodic, and random phase characteristics. Traditional differential protection is designed for high-current applications at the power frequency kilovolt level, relying on amplitude and phase balance logic for differential calculation. Directly applying the original algorithm renders the balance logic ineffective. 2. The unit grounding structure does not meet the design conditions for differential circulation current: Turbine bearing faults are mostly single-point high-resistance grounding faults. The fault circuit does not form a closed circulation current path, and the differential difference changes only slightly before and after the fault. Existing differential algorithms struggle to identify the slow degradation process of bearing insulation, making early warning of potential hazards impossible. 3. Difficulty in isolating common-mode interference: Unit operating vibration, momentary poor contact of carbon brushes, and excitation side harmonic interference can simultaneously couple to two current acquisition points. Conventional differential algorithms cannot distinguish between false differential values ​​caused by common-mode interference and valid differential data generated by real faults, easily leading to malfunctions due to interference. 4. Lack of braking algorithms adapted to dynamic shaft current conditions: Shaft current fluctuates in real time with unit output, speed, and oil film aging. Traditional differentials use a fixed braking threshold, which cannot simultaneously meet the requirements of sensitivity to small-load faults and anti-interference under large-scale conditions. 5. Traditional differentials only distinguish between faults within and outside the protection zone, lacking segmented location capability: Conventional differentials can only determine whether a fault is within or outside the protection zone, and cannot perform fine-grained segmented location of the three types of bearing faults (upper guide, water guide, and lower guide), failing to meet the actual usage requirements of component-by-component maintenance in hydropower stations.

[0007] Due to the aforementioned technical deficiencies, existing shaft current protection equipment is unable to meet the high standards of safety management and control requirements of current power countermeasures regulations. The potential for deterioration in the insulation of the unit bearings is prone to missed or false alarms. This can lead to unplanned shutdowns causing economic losses to the hydropower plant, or even major equipment accidents such as bearing bush burnout and main shaft magnetization. Therefore, it is urgent to develop a practical differential protection solution that is compatible with the shaft current operating conditions of hydropower turbines to address the various shortcomings of existing technologies. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a turbine shaft current differential protection device and method for accurately locating fault points. It addresses the technical shortcomings of existing single-CT shaft current protection, such as single judgment criteria, easy false activation, inability to locate fault points, and difficulty in adapting traditional differential protection to the operating conditions of turbine shaft current. By relying on dual-CT synchronous differential acquisition, three-stage adaptive braking algorithm, and four-dimensional fault location judgment, it achieves anti-interference operation and accurate fault zone location, overcomes the shortcomings of existing technology, and fills the gap in domestic shaft current differential protection technology.

[0009] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A turbine shaft current differential protection device for accurately locating fault points includes a dual-channel current transformer acquisition component, a 16-bit high-speed synchronous analog-to-digital acquisition unit, a 32-bit ARM main control processing unit, a human-machine interaction unit, a switch output unit, an analog output unit, a communication unit, and a wide-temperature isolation power supply unit. The dual-current transformer acquisition assembly includes a first current transformer and a second current transformer. The first current transformer is installed at the grounding terminal of the turbine shaft to acquire the total shaft current I1, and the second current transformer is installed on the grounding carbon brush circuit to acquire the carbon brush return current I. t ; The 16-bit high-speed synchronous analog-to-digital acquisition unit is electrically connected to two sets of current transformers to synchronously complete I1 and I2. t Two current signals are sampled in parallel. The 32-bit ARM main control processing unit is electrically connected to the analog-to-digital acquisition unit, the human-machine interface unit, the digital output unit, the analog output unit, and the communication unit, respectively, and is used to receive sampled data and calculate the differential current I. d =I1 I t Braking current, built-in protection logic and fault location criteria, drive the corresponding output circuit to act according to the calculation results; The wide-temperature isolated power supply unit provides isolated power to all electrical components of the device.

[0010] The aforementioned analog-to-digital acquisition unit uses the AD7606 acquisition chip, which has multi-channel synchronous acquisition capability, a single-channel sampling rate of not less than 200kSPS, and a two-channel current synchronous acquisition error of ≤1μs; the main control unit has a built-in digital filtering algorithm to perform second-order Butterworth low-pass filtering superimposed with 50-point moving average filtering on the acquired current.

[0011] The aforementioned ARM main control unit uses the STM32F103ZET6 control chip, which is equipped with on-chip flash memory and storage units for storing fault waveform data, protection settings, and historical operating parameters. The device has fault component discrimination logic, which uses the current difference ΔI between consecutive cycles. d Mutation signature open protection on / off.

[0012] The above-mentioned wide-temperature isolation power supply unit operates in a temperature range of -40℃ to +70℃, has a power isolation withstand voltage of ≥4000V AC, a power conversion efficiency of not less than 90%, and integrates overvoltage, overcurrent, and short-circuit hardware protection circuits.

[0013] The aforementioned human-machine interface unit includes an industrial touchscreen display and multiple status indicator lights. The touchscreen resolution is 800×480, and it displays I1 and I2 status indicators in real time. t Differential current I dBraking current value, fault location, and protection action information.

[0014] The aforementioned digital output unit is equipped with at least four independent passive contacts, which are compatible with AC 220V / 0.5A and DC 220V / 0.2A load specifications, and are used for fault alarm output and unit trip drive output, respectively; the analog output unit is equipped with at least two 4-20mA standard analog signal output channels to realize remote transmission of shaft current and differential current.

[0015] The aforementioned communication unit integrates an RS485 bus interface and an Ethernet interface, and its communication protocols are compatible with Modbus-RTU and Modbus-TCP, enabling data interaction between the local device and the power plant's supervisory control system.

[0016] The aforementioned ARM main control unit has an embedded three-stage adaptive braking characteristic algorithm. The braking threshold dynamically changes with the real-time braking current Ires and automatically generates a differentiated action setting value Iop. The three-stage braking logic is as follows: 1) Braking current I res When <500mA, the action threshold I op Fixed at 200mA; 2) 500mA≤I res When <1000mA, I op =200+0.4×(I res 500) linear change; 3) I res At ≥1000mA, the action threshold I op Fixed at 400mA; When the differential current I d ≥I op Timely determination of faults within the equipment area.

[0017] The aforementioned ARM main control unit incorporates a four-dimensional fault location judgment logic, based on I1, I... t I d Parameter combinations distinguish between fault location and fault type: 1) I1 and I t If the values ​​are equal and I1 exceeds the alarm threshold, it is determined that the insulation of the upper guide bearing is deteriorated, and the device issues an alarm signal. 2) I1 and I t If the values ​​are equal and I1 exceeds the action threshold, it is determined that the upper guide bearing insulation has broken down, and the device drives the protection action. 3) I1 exceeds the alarm threshold and I d If the value exceeds the set value, it is determined that the oil film of the water guide / lower guide bearing is damaged, a fixed-point alarm is triggered, and the fault location is marked. 4) I1 exceeds the action threshold and Id If the value exceeds the set value, it is determined that the upper guide bearing and the water guide / lower guide bearing are synchronously faulty, the device protection outlet is activated and the two fault points are accurately located.

[0018] A method for differential protection of turbine shaft current based on the above-mentioned device includes the following steps: S1. The device is powered on and completes hardware self-test, automatically calibrates zero drift and gain error of the acquisition channel, and loads preset protection settings. S2, synchronously acquire the shaft current I1 and the grounding carbon brush circuit current I through dual-channel current transformers. t After analog-to-digital conversion and digital filtering, the signal is sent to the main control unit. S3, Main control unit calculates differential current I d =I1 I t With braking current I res Based on a three-stage adaptive braking model, dynamic action threshold I is generated in real time. op ; S4. Compare I1 and I using a combination of four-dimensional criteria. t I d I op The numerical values ​​are used to determine the fault type and pinpoint the fault location to the upper guide bearing or the water guide / lower guide bearing. S5. Based on the fault determination result, selectively output alarm signals or tripping action signals, synchronously store fault waveform data, and upload fault information to the monitoring backend via the communication unit.

[0019] In step S2, the synchronous sampling rate is not less than 200 kSPS, the synchronous error of the two current sampling channels is controlled within 1 μs, and a second-order Butterworth low-pass filter combined with a 50-point moving average algorithm is used to filter out high-frequency interference noise on site.

[0020] Step S3 introduces fault component discrimination logic, which only detects fault components in the differential current change ΔI. d The protection is activated when there is a sudden increase in synchronous current, which helps to suppress maloperation of the protection caused by carbon brush leakage current and slow temperature drift.

[0021] The method also includes an extended monitoring step, where the device is connected to an external shaft voltage acquisition signal, and the shaft voltage data and shaft current differential data are fused to form a dual-parameter joint fault determination logic to improve fault identification accuracy.

[0022] After the device completes the protection action, it automatically records the time of the fault occurrence, the location of the fault, the electrical parameters of the fault, and the action type. The fault waveform data is stored locally and simultaneously sent to the power plant monitoring system remotely.

[0023] The adaptive braking curve is used in conjunction with the four-dimensional zone fault location criteria. It relies on the dynamic threshold to avoid common-mode interference caused by unit load fluctuations, excitation harmonics, and poor carbon brush contact, and relies on the current ratio relationship to achieve multi-bearing fault zone location.

[0024] The present invention relates to a turbine shaft current differential protection device and method for accurately locating fault points. The present invention has the following outstanding technical advantages: 1. Pioneering a dual-CT differential protection architecture for turbine shaft current, filling a technological gap in the industry: Breaking the inherent technical prejudice in the industry that "differential protection cannot be used for shaft current protection", the differential protection principle is applied to the monitoring scenario of weak shaft current at the microampere to milliampere level. It solves the inherent defect of single CT having a single criterion from the principle level, greatly improves the overall reliability of protection, and meets the mandatory requirements of power countermeasures specifications; 2. Three-stage adaptive braking characteristics significantly improve anti-interference capability: The action threshold is dynamically segmented and adjusted according to the operating conditions of the group. The low threshold under light load ensures sensitive detection of small faults, while the high threshold under large interference suppresses maloperation caused by leakage current, noise, and poor carbon brush contact, thus solving the pain point that the sensitivity and prevention of maloperation of traditional fixed threshold protection cannot be balanced. 3. Four-dimensional combined criteria for accurate fault location: Different faults in the upper guide and water / lower guide bearings are distinguished by the current ratio of the two currents, which changes the traditional protection that can only alarm but not pinpoint the fault. After a fault occurs, the faulty component is directly locked, which greatly shortens the unit maintenance downtime and reduces the economic loss of power generation. 4. Dual anti-maloperation design with multiple filtering and fault component blocking: High-speed synchronous hardware acquisition combined with dual-layer digital filtering, superimposed with fault component change quantity open protection logic, effectively filters out common-mode interference caused by excitation harmonics and mechanical vibration, and further avoids protection tripping caused by non-fault factors; 5. Industrial-grade wide-temperature isolation hardware design with strong environmental adaptability: The whole unit power supply operates in a wide temperature range of -40℃ to +70℃, with 4000VAC high-voltage isolation, making it suitable for the humid, temperature-different, and electromagnetically complex field conditions of hydropower stations; multiple analog, switch, and communication interfaces can be seamlessly connected to the existing monitoring systems of power plants, making it highly versatile. 6. Expandable shaft voltage joint monitoring: A shaft voltage access channel is reserved to realize the collaborative judgment of shaft current and shaft voltage dual parameters, further optimize the fault identification accuracy, and provide ample room for product upgrade and expansion. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the primary circuit and dual CT installation arrangement of the device of the present invention; Figure 2 This is a block diagram of the hardware architecture of the shaft current differential protection device of the present invention; Figure 3 This is a flowchart illustrating the overall workflow of the differential protection method for turbine shaft current of the present invention. Figure 4 This is a schematic diagram of the three-segment adaptive braking characteristic curve of the present invention. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0027] Example 1: This invention provides a turbine shaft current differential protection device and method for accurately locating fault points. Based on dual-CT synchronous differential acquisition, a three-stage adaptive braking algorithm, and four-dimensional fault location criteria, it achieves anti-interference operation and precise fault location by zone, overcoming the shortcomings of existing technologies and filling the gap in domestic shaft current differential protection technology. The technical solution is as follows: I. Hardware Components of the Protection Device It mainly includes: a dual-channel current transformer acquisition component, a 16-bit high-speed synchronous analog-to-digital converter (AD) acquisition unit, a 32-bit ARM main control processing unit, a human-machine interaction unit, a digital output unit, an analog output unit, a communication unit, and a wide-temperature, high-isolation power supply unit.

[0028] The dual-current transformer acquisition assembly includes a first current transformer CT1 and a second current transformer CT2. CT1 is installed at the grounding terminal of the turbine shaft to acquire the total shaft current I1. CT2 is installed on the grounding carbon brush circuit to acquire the carbon brush return current I. t .

[0029] The 16-bit high-speed synchronous AD acquisition unit is electrically connected to CT1 and CT2 to realize I1 and I t Two-channel current synchronous sampling and conversion; the AD acquisition unit uses the AD7606 chip, which has 8-channel synchronous acquisition capability, single-channel sampling rate ≥200kSPS, and two-channel current synchronous acquisition error ≤1μs.

[0030] The 32-bit ARM main control processing unit uses the STM32F103ZET6 main control chip with a main frequency of 72MHz. It is equipped with on-chip flash memory and EEPROM storage units, which are electrically connected to the AD acquisition unit, human-machine interaction unit, digital output unit, analog output unit, and communication unit, respectively. The main control unit has built-in digital filtering program, adaptive braking algorithm, four-dimensional fault location criteria, and fault component discrimination logic. After receiving the sampled data, it performs differential current and braking current calculations, drives the operation of each output unit according to the logic judgment results, and stores fault waveforms and operating parameters.

[0031] The wide-temperature, high-isolation power supply unit provides operating power to all components of the device. The power supply operating temperature range is -40℃ to +70℃, the isolation withstand voltage is ≥4000VAC, the power conversion efficiency is ≥90%, and it integrates overvoltage, overcurrent, and short-circuit hardware protection circuits.

[0032] The human-machine interface unit consists of a 5-inch 800×480 resolution industrial touchscreen and multiple LED status indicators. The touchscreen displays I1 and I2 status indicators in real time. t Differential current I d Braking current I res The fault location and protection action status are displayed intuitively by LED indicator lights, showing the device's operation, alarm, and trip status.

[0033] The digital output unit is equipped with at least four independent passive contacts, which are compatible with DC220V / 0.2A and AC220V / 0.5A electrical loads for external fault alarm and unit tripping circuits; the analog output unit is equipped with at least two 4-20mA standard current output channels to realize I1, I... d Analog signals are transmitted remotely to the central control equipment.

[0034] The communication unit integrates RS485 and Ethernet dual interfaces, and is compatible with Modbus RTU and Modbus TCP communication protocols, enabling data interaction between the device and the power plant's supervisory control system, as well as remote transmission of fault information.

[0035] The ARM main control unit has a built-in digital filtering algorithm that uses a second-order Butterworth low-pass filter superimposed with a 50-point moving average filter to process the sampled current signal, filtering out high-frequency noise and harmonic interference from the field. At the same time, it sets up fault component discrimination logic, using the sudden change characteristic of the current difference ΔId between adjacent cycles as the protection opening condition, and only activates fault discrimination when the differential current change increases synchronously, avoiding protection maloperation caused by slow carbon brush leakage and component temperature drift.

[0036] The ARM main control unit embeds a three-stage adaptive braking characteristic algorithm, based on the real-time braking current I. res Dynamic calculation of protection action threshold I op Specific segmentation logic: ① Low current region: I res <500mA, Action Threshold I op A fixed value of 200mA is used to ensure that minor faults can be detected sensitively under light load conditions of the unit. ② Transition linear region: 500mA≤I res <1000mA, Action Threshold I op =200+0.4×(I res 500), the threshold value increases linearly with the braking current, balancing protection sensitivity and anti-interference performance; ③ High current region: I res ≥1000mA, Action Threshold I op A fixed value of 400mA is used to suppress maloperation of the protection system under heavy load and strong common-mode interference conditions of the unit. Protection action judgment condition: when the differential current I d ≥I op At that time, it was determined that the unit had experienced a fault within the protected area.

[0037] The ARM main control unit has a built-in four-dimensional fault location criterion, relying on I1 and I2. t I d The relationship between the three numerical values ​​distinguishes the location and severity of the fault, with specific criteria as follows: 1) I1 and I t If the values ​​are equal and I1 exceeds the alarm setting value: it is determined that the insulation of the upper guide bearing is deteriorated, and the device outputs an alarm signal; 2) I1 and I t If the values ​​are equal and I1 exceeds the action setting value: it is determined that the upper guide bearing insulation has broken down, and the device drives the switch output to operate. 3) I1 exceeds the alarm setting value, and I d If the fault exceeds the fault setting threshold: it is determined that the lubricating oil film of the water guide / lower guide bearing is damaged, a fixed alarm is triggered and the fault location is marked; 4) I1 exceeds the action setpoint, and I d If the fault setting threshold is greater than 1, the upper guide bearing and the water guide / lower guide bearing are determined to be synchronously faulty. The device protection trips and the fault location is located twice.

[0038] II. Turbine shaft current differential protection method based on the above-mentioned device This invention also claims protection for a shaft current differential protection method implemented using the above-described device, comprising the following steps: S1. The device is powered on and started, completes the hardware self-test, automatically calibrates the zero drift error and gain error of the AD acquisition channel, and loads the pre-set protection settings and braking parameters. S2, synchronously acquire the main shaft current I1 and the grounding carbon brush current I through CT1 and CT2.t The AD7606 performs analog-to-digital conversion at a rate of ≥200kSPS with a synchronization error of ≤1μs. The sampled data is then sent to the ARM main controller after passing through a second-order Butterworth low-pass filter and a 50-point moving average digital filter. S3, Main control unit calculates differential current I d =I1 I t Based on the braking current Ires, a dynamic action threshold I is generated in real time using a three-stage adaptive braking model. op Combined with the fault component discrimination logic, the subsequent fault determination process is only enabled when ΔId undergoes a sudden change. S4. The main control calls the four-dimensional fault location criteria, combined with I1 and I... t I d I op The parameters complete the identification of fault type and fault location, distinguishing whether the fault is located in the upper guide bearing or the water guide / lower guide bearing; S5. Based on the fault determination result, selectively drive the switch output alarm signal or trip action signal, and synchronously transmit electrical parameters through the analog channel; the device locally stores the fault occurrence time, fault location, and fault waveform data, and uploads the fault information to the power plant monitoring background through the communication unit.

[0039] Preferably, the protection method of the present invention also includes an extended monitoring step: the device has a reserved shaft voltage signal acquisition interface, which can be connected to an external shaft voltage monitoring circuit, and the shaft voltage parameters and shaft current differential parameters are integrated to form a dual-dimensional joint fault discrimination logic, thereby further improving the accuracy of fault identification.

[0040] Example 2: Device hardware implementation The equipment installation is completed on the primary circuit of the hydro-generator unit: the turbine shaft → upper guide bearing → water guide / lower guide bearing → grounding carbon brush → earth form the main shaft grounding circuit; CT1 is snap-fitted and fixed at the grounding end of the turbine shaft, and CT2 is installed and fixed on the grounding carbon brush lead cable; the AD7606 acquisition board is connected to the secondary outputs of CT1 and CT2 respectively; the STM32F103ZET6 main control board, AD acquisition board, touch screen, LED indicator, switch relay, 4~20mA transmitter module, RS485 and Ethernet module are connected in sequence; the wide-temperature isolation power supply is connected to the power plant's DC 220V operating power supply to power all the boards of the whole machine.

[0041] Human-machine interface touch screen configuration I1, I t I d I resThe system includes a real-time data display interface, a fault alarm pop-up interface, and a setting interface; four passive contact points for digital outputs are connected to the unit fault alarm, upper guide fault trip, water guide fault alarm, and main outlet trip circuits; two 4~20mA analog terminals are connected to the central control PLC analog input card; an RS485 bus is connected to the power plant's local measurement and control device, and an Ethernet connection is connected to the power plant's host computer network switch.

[0042] Example 3: Implementation of on-site operation methods for the equipment S1: When the device is powered on, it automatically performs self-tests on the power supply, AD channel, and communication circuit. After the hardware is found to be normal, it automatically calibrates the zero drift and gain of each acquisition channel and imports preset parameters: alarm threshold, action threshold, and three-stage braking segment parameters. S2: CT1 and CT2 are continuously and synchronously sampled. AD7606 synchronously converts the current signal at a rate of 200kSPS. The sampled data is filtered by a second-order Butterworth low-pass filter and a 50-point moving average filter to remove high-frequency interference from the field. S3: ARM main control real-time computing d =I1 I t Braking current I res The action threshold I is refreshed in real time according to the three-stage braking formula. op ΔI is calculated synchronously. d Differential change, only ΔI d Enable fault detection logic when a sudden change in the quantity occurs; S4: Example of parameter matching criterion: ① Actual measurement I1=I t And I1 > alarm value → upper conductor insulation aging, touch screen pop-up window upper conductor insulation reduction alarm, corresponding alarm contact closes; ② Actual measurement I1=I t And I1 > action value → upper conductor insulation breakdown, trip contact closure triggers unit protection action; ③ Actual measured I1 exceeds alarm value, I d > Setting threshold → Water guide bearing oil film damage, local indicator light illuminates, and fixed-point fault signal is uploaded; ④ Actual measured I1 over-action value, I d > Setting threshold → Combined fault in upper and lower bearings, device output trips and double fault point marking; S5: The device automatically stores the waveform data before and after the fault occurs and uploads the fault type, fault location, and fault current to the power plant monitoring backend via Ethernet / 485.

Claims

1. A turbine shaft current differential protection device for accurately locating fault points, characterized in that, It includes a dual-channel current transformer acquisition component, a synchronous analog-to-digital acquisition unit, a main control processing unit, a human-machine interaction unit, a digital output unit, an analog output unit, a communication unit, and a wide-temperature isolation power supply unit; The dual-channel current transformer acquisition assembly includes a first current transformer and a second current transformer. The first current transformer is installed at the grounding terminal of the turbine shaft to acquire the total shaft current I1, and the second current transformer is installed on the grounding carbon brush circuit to acquire the carbon brush return current I. t ; The synchronous analog-to-digital acquisition unit is electrically connected to two sets of current transformers to synchronously complete I1 and I t Two current signals are sampled in parallel. The main control processing unit is electrically connected to the analog-to-digital acquisition unit, the human-machine interaction unit, the digital output unit, the analog output unit, and the communication unit, respectively, and is used to receive sampled data and calculate the differential current I. d =I1 I t Braking current, built-in protection logic and fault location criteria, drive the corresponding output circuit to act according to the calculation results; The wide-temperature isolated power supply unit provides isolated power to all electrical components of the device.

2. The turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The analog-to-digital acquisition unit uses the AD7606 acquisition chip, which has multi-channel synchronous acquisition capability, a single-channel sampling rate of not less than 200kSPS, and a two-channel current synchronous acquisition error of ≤1μs; the main control unit has a built-in digital filtering algorithm to perform second-order Butterworth low-pass filtering superimposed with 50-point moving average filtering on the acquired current.

3. The turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The main control unit uses an STM32F103ZET6 control chip, which is equipped with on-chip flash memory and storage units for storing fault waveform data, protection settings, and historical operating parameters. The device has fault component discrimination logic, which uses the current difference ΔI between the previous and subsequent cycles. d Mutation signature open protection on / off.

4. The turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The wide-temperature isolation power supply unit operates in a temperature range of -40℃ to +70℃, has a power isolation withstand voltage of ≥4000V AC, a power conversion efficiency of not less than 90%, and integrates overvoltage, overcurrent, and short-circuit hardware protection circuits.

5. A turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The human-machine interface unit includes an industrial touch screen display and multiple status indicator lights. The touch screen has a resolution of 800×480 and displays I1 and I2 status indicators in real time. t Differential current I d Braking current value, fault location, and protection action information.

6. The turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The aforementioned digital output unit is equipped with at least four independent passive contacts, which are compatible with AC 220V / 0.5A and DC 220V / 0.2A load specifications, and are used for fault alarm output and unit trip drive output, respectively; the aforementioned analog output unit is equipped with at least two 4-20mA standard analog signal output channels to realize remote transmission of shaft current and differential current.

7. A turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The communication unit integrates an RS485 bus interface and an Ethernet interface, and the communication protocol is compatible with Modbus-RTU and Modbus-TCP, enabling data interaction between the local device and the power plant's supervisory control system.

8. A turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The main control unit is embedded with a three-stage adaptive braking characteristic algorithm, and the braking threshold follows the real-time braking current I. res Dynamic changes, automatically generating differentiated action setpoints I op ; The three-stage braking logic is as follows: 1) Braking current I res When <500mA, the action threshold I op Fixed at 200mA; 2) 500mA≤I res When <1000mA, I op =200+0.4×(I res 500) linear change; 3) I res At ≥1000mA, the action threshold I op Fixed at 400mA; When the differential current I d ≥I op Timely determination of faults within the equipment area.

9. A turbine shaft current differential protection device for accurately locating fault points according to claim 1, characterized in that, The main control unit has a built-in four-dimensional fault location judgment logic, based on I1, I t I d Parameter combinations distinguish between fault location and fault type: 1) I1 and I t If the values ​​are equal and I1 exceeds the alarm threshold, it is determined that the insulation of the upper guide bearing is deteriorated, and the device issues an alarm signal. 2) I1 and I t If the values ​​are equal and I1 exceeds the action threshold, it is determined that the upper guide bearing insulation has broken down, and the device drives the protection action. 3) I1 exceeds the alarm threshold and I d If the value exceeds the set value, it is determined that the oil film of the water guide / lower guide bearing is damaged, a fixed-point alarm is triggered, and the fault location is marked. 4) I1 exceeds the action threshold and I d If the value exceeds the set value, it is determined that the upper guide bearing and the water guide / lower guide bearing are synchronously faulty, the device protection outlet is activated and the two fault points are accurately located.

10. A method for differential protection of turbine shaft current based on the device described in any one of claims 1 to 9, characterized in that, It includes the following steps: S1. The device is powered on and completes hardware self-test, automatically calibrates zero drift and gain error of the acquisition channel, and loads preset protection settings. S2, synchronously acquire the shaft current I1 and the grounding carbon brush circuit current I through dual-channel current transformers. t After analog-to-digital conversion and digital filtering, the signal is sent to the main control unit. S3, Main control unit calculates differential current I d =I1 I t With braking current I res Based on a three-stage adaptive braking model, dynamic action threshold I is generated in real time. op ; S4. Compare I1 and I using a combination of four-dimensional criteria. t I d I op The numerical values ​​are used to determine the fault type and pinpoint the fault location to the upper guide bearing or the water guide / lower guide bearing. S5. Based on the fault determination result, selectively output alarm signals or tripping action signals, synchronously store fault waveform data, and upload fault information to the monitoring backend via the communication unit.

11. The method for differential protection of turbine shaft current according to claim 10, characterized in that: In step S2, the synchronous sampling rate is not less than 200 kSPS, the synchronous error of the two current sampling channels is controlled within 1 μs, and a second-order Butterworth low-pass filter combined with a 50-point moving average algorithm is used to filter out high-frequency interference noise on site.

12. The method for differential protection of turbine shaft current according to claim 10, characterized in that: Step S3 introduces fault component discrimination logic, which only detects fault components in the differential current change ΔI. d The protection is activated when there is a sudden increase in synchronous current, which helps to suppress maloperation of the protection caused by carbon brush leakage current and slow temperature drift.

13. The method for differential protection of turbine shaft current according to claim 10, characterized in that: The method also includes an extended monitoring step, where the device is connected to an external shaft voltage acquisition signal, and the shaft voltage data and shaft current differential data are fused to form a dual-parameter joint fault determination logic to improve fault identification accuracy.

14. The method for differential protection of turbine shaft current according to claim 10, characterized in that: After the device completes the protection action, it automatically records the time of the fault occurrence, the location of the fault, the electrical parameters of the fault, and the action type. The fault waveform data is stored locally and simultaneously sent to the power plant monitoring system remotely.

15. The method for differential protection of turbine shaft current according to claim 10, characterized in that: The adaptive braking curve is used in conjunction with the four-dimensional zone fault location criteria. It relies on the dynamic threshold to avoid common-mode interference caused by unit load fluctuations, excitation harmonics, and poor carbon brush contact, and relies on the current ratio relationship to achieve multi-bearing fault zone location.

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